Reduced stem growth, but no reserve depletion or hydraulic impairment in beech suffering from long-term decline

Abstract

Keymessage Under non-extreme drought conditions, reduced stem growth is not associated with reserve or hydraulic impairment in beech suffering from longterm decline. Abstract Global change is expected to increase the frequency and the intensity of drought events in temperate ecosystems. In some regions, this might be associated with an increase in tree decline. Of the ecophysiological mechanisms that have been proposed to explain tree decline, an impairment of the vascular transport system and/or carbon function are two of the most discussed. In a context of long-term decline caused by droughts, we investigated the functional differences between the carbon, nitrogen, and hydraulic functions of healthy and declining mature beech (Fagus sylvatica L.) trees. The study was carried out over two consecutive years with contrasting water availabilities. The radial growth of declining trees was clearly less than that of healthy trees, due to a lower growth rate, associated during the wet year with a shorter growth period. Leaf functional characteristics and hydraulic parameters (native embolism and cavitation vulnerability curves) were similar in healthy and declining trees. However, at the end of a growing season characterized by a dry spring, carbon reserves concentrations in young branches of declining trees were lower than those in healthy trees, though they recovered during the following non-constraining growing season. Our results did not indicate carbon starvation, nitrogen deficiency, or hydraulic failure. However, there seems to be some compensation mechanism related to reserve dynamics in the remaining living tissue of the declining trees. This study shows that the climate conditions of successive years are probably crucial for these functional adjustments to be operational.

Low Growth Sensitivity and Fast Replenishment of Non-structural Carbohydrates in a Long-Lived Endangered Conifer After Drought

“…However, C allocation after drought remains largely unknown for trees under natural conditions. One of the few studies analyzing C allocation in mature trees after drought, found that the trunk sapwood and phloem NSC concentrations in Fagus sylvatica did not increase in a year of normal precipitation with regard to a previous dry year, although branch NSC concentrations did (Delaporte et al, 2016). However, growth recovery was found to be greater than the increase in branch NSC concentrations (Delaporte et al, 2016).…”

“…One of the few studies analyzing C allocation in mature trees after drought, found that the trunk sapwood and phloem NSC concentrations in Fagus sylvatica did not increase in a year of normal precipitation with regard to a previous dry year, although branch NSC concentrations did ( Delaporte et al, 2016 ). However, growth recovery was found to be greater than the increase in branch NSC concentrations ( Delaporte et al, 2016 ). While this study suggests that the rebuilt of storage after drought does not occur at the expens of growth, droughts could cause C storage reductions in other systems, particularly in isohydric species ( McDowell et al, 2008 , 2011 ; Brodribb et al, 2014 ).…”

Fine-scale mapping of sapwood anatomical properties reveals plasticity in hydraulics during water deficit

“…Changes in stem cavitation resistance under prolonged water deficit conditions (such as those observed in this study) are not a common functional response in many species (e.g. Martin -StPaul et al 2013;Delaporte et al 2015), but under certain water deficit conditions that permit continued albeit diminished expansive growth in sapwood tissues, this may eventually affect whole stem cavitation resistance. Further research is needed to understand the capacity for temporal changes in cavitation resistance in species experiencing long-term reductions in water availability (Anderegg 2015).…”

Changing climatic sensitivity and effects of drought frequency on the radial growth of Fagus sylvatica at the xeric frontiers of Central Europe

“…Under optimal conditions, basal area growth curves increase almost monotonously, but later asymptotically with age. Decreasing trend usually appears when approaching the end of the individual beech tree's lifetime, therefore, clearly reduced stem growth rates can be a (predictive) sign of a longterm decline (Piovesan et al, 2008;Gillner et al, 2013;Delaporte et al, 2016). In comparison to other, especially to norther sites, some of the REZI trees underwent a drastic growth reduction, that could be interpreted as a predictive sign of vitality loss, which lead to drought-induced mortality event accounting also for the later sanitary interventions.…”